Planck pre-launch status: calibration of the Low Frequency Instrument flight model radiometers

TL;DR

This paper details the comprehensive on-ground calibration process of the Planck satellite's Low Frequency Instrument radiometers, ensuring their readiness and performance understanding before launch.

Contribution

It presents the calibration methodology and results for all eleven RCAs, including measurements of noise, gain, spectral response, and thermal susceptibility, crucial for data analysis.

Findings

Measured noise temperature and gain for each RCA

Assessed spectral response and thermal susceptibility

Provided calibration parameters for data analysis

Abstract

The Low Frequency Instrument (LFI) on-board the ESA Planck satellite carries eleven radiometer subsystems, called Radiometer Chain Assemblies (RCAs), each composed of a pair of pseudo-correlation receivers. We describe the on-ground calibration campaign performed to qualify the flight model RCAs and to measure their pre-launch performances. Each RCA was calibrated in a dedicated flight-like cryogenic environment with the radiometer front-end cooled to 20K and the back-end at 300K, and with an external input load cooled to 4K. A matched load simulating a blackbody at different temperatures was placed in front of the sky horn to derive basic radiometer properties such as noise temperature, gain, and noise performance, e.g. 1/f noise. The spectral response of each detector was measured as was their susceptibility to thermal variation. All eleven LFI RCAs were calibrated. Instrumental parameters measured in these tests, such as noise temperature, bandwidth, radiometer isolation, and linearity, provide essential inputs to the Planck-LFI data analysis.